The present invention relates to polymeric powders suitable for use as electrostatographic toners and, more particularly, to a method for forming electrostatographic toner particles comprising a quaternary ammonium tetraphenylborate salt and a polymeric phosphonium salt that operate to control the morphology of the toner particles.
Electrostatic toner polymer particles are commonly prepared by a process referred to as xe2x80x9climited coalescencexe2x80x9d. In this process, polymer particles having a narrow size distribution are obtained by forming a solution of a polymer in a solvent that is immiscible with water, dispersing the solution so formed in an aqueous medium containing a solid colloidal stabilizer and removing the solvent by evaporation. The resultant particles are then isolated, washed and dried.
In the practice of this technique, toner particles are prepared from any type of polymer that is soluble in a water-immiscible solvent. Thus, the size and size distribution of the resulting particles can be predetermined and controlled by the relative quantities of the particular polymer employed, the solvent, the quantity and size of the water insoluble solid particulate suspension stabilizer, typically silica or latex, and the size to which the solvent-polymer droplets are reduced by agitation.
Limited coalescence techniques of this type have been described in numerous patents pertaining to the preparation of electrostatic toner particles because such techniques typically result in the formation of toner particles having a substantially uniform size distribution. Representative limited coalescence processes employed in toner preparation are described in U.S. Pat. Nos. 4,833,060 and 4,965,131, the disclosures of which are incorporated herein by reference.
The shape of the toner particles has a bearing on electrostatic toner transfer and cleaning properties. Thus, for example, the transfer and cleaning efficiency of toner particles have been found to improve as the sphericity of the particles are reduced. Thus far, workers in the art have long sought to modify the shape of the evaporative limited coalescence type toners independently of pigment, binder, or charge agent choice in order to enhance the cleaning and transfer properties of the toner.
U.S. Pat. No. 5,283,151 is representative of the prior art in this field and described the use of carnauba wax to modify toner morphology. The method comprises the steps of dissolving carnauba wax in ethyl acetate heated to a temperature of at least 75xc2x0 C. and cooling the solution, resulting in the precipitation of the wax in the form of very fine needles a few microns in length; recovering the wax needles and mixing them with a polymer material, a solvent, a charge control agent, and, optionally, a pigment to form an organic phase; dispersing the organic phase in an aqueous phase comprising a particulate stabilizer and homogenizing the mixture; and evaporating the solvent and washing and drying the resultant product.
This technique, however, requires the use of elevated temperature to dissolve the wax in the solvent, followed by cooling the solution to precipitate the wax. The wax does not stay in solution in ethyl acetate at ambient temperature, which makes scale-up of this method very difficult.
Tetraphenylborate quaternary salts have been employed as charge control agents for electrophotographic toners. For example, U.S. Pat. Nos. 5,194,472 and 5,516,616 disclose quaternary ammonium salt charge control agents, including tetraphenylborates, that contain ester moieties. U.S. Pat. Nos. 5,075,190 and 5,041,625 disclose mono- and bis-pyridinium tetraphenylborate charge control agents, and U.S. Pat. No.5,482,741 describes a process for absorbing a charge control agent such as potassium tetraphenylborate onto flow aid particles. Also, JP 91-41021 discloses an image-forming method using a toner containing various kinds of tetraarylborates as charge control-agents.
Polymeric phosphonium salts are known as components of xerographic or electrostatic toner particles. For example, both U.S. Pat. Nos. 4,837,394 and 4,855,396 both disclose toner particles in which quaternary phosphonium salt moieties are covalently bound to polyesters.
Thus, although both tetraphenylborate quaternary ammonium salts and polymeric phosphonium salts have been individually employed in toner particles, their use in combination as shape control agents in the limited coalescence process for making toner particles is not known.
The present invention is directed to a process for forming non-spherical toner particles by limited coalescence comprises: forming an organic phase comprising a polymeric material, a pigment, a quaternary ammonium tetraphenylborate salt, a phosphonium salt polymer formed by condensation of at least one dicarboxylic acid or dicarboxylic ester monomer with at least one diol monomer, at least one of the acid or ester monomers including a triarylphosphonium salt group, and a water-immiscible liquid; dispersing the organic phase in an aqueous phase containing a solid colloidal stabilizer; forming a suspension of small droplets of the organic phase in the aqueous phase by high shear agitation; removing the water-immiscible liquid from the small droplets, thereby forming a suspension of small solid particles in the aqueous phase; and separating and drying the solid particles, which are toner particles having a non-spherical shape.
The present invention relates to a method for the preparation of polymeric powders suitable for use as electrostatographic toner, and more particularly, to a method for preparation of toner particles of controlled shape and charge in which certain quaternary ammonium tetraphenylborate salts, in combination with a phosphonium salt polymer formed by condensation of at least one dicarboxylic acid or dicarboxylic ester monomer with at least one diol monomer, wherein at least one of the acid or ester monomers includes a triarylphosphonium salt group, are introduced into the organic phase of a limited coalescence process to control the morphology of the particles and to function as charge control agents.
In accordance with the present invention, the pigment can be provided as a dispersion, prepared by conventional techniques as, for example, media milling, melt dispersion and the like. The pigment dispersion, polymeric material, quaternary ammonium tetraborate salt, water-immiscible solvent, and, optionally, an additional charge control agent are combined to form an organic phase in which the pigment concentration ranges from about 1 to about 40 weight percent, preferably, about 4 to about 20 weight percent, based upon the total weight of solids. The optional charge control agent is employed in an amount up to about 10 weight percent, preferably about 0.2 to about 5 weight percent, based on the total weight of solids. Suitable charge control agents are disclosed, for example, in U.S. Pat. Nos. 3,893,935, 4,323,634, and 4,079,014, and British Patent No. 1,420,839.
The solvents chosen for use in the organic phase steps may be selected from among any of the well-known solvents capable of dissolving polymers of the type employed herein. Typical of the solvents chosen for this purpose are dichloromethane, ethyl acetate, methyl ethyl ketone, and the like.
The organic phase is permitted to stir, typically overnight, and then dispersed in an aqueous phase comprising a particulate stabilizer and, optionally, a promoter. The aqueous phase may have a pH of about 2 to about 7 but preferably is buffered to a pH of about 4.
The particulate stabilizer may be selected from silicon dioxide or from highly cross-linked polymeric latex materials of the type described in the previously mentioned U.S. Pat. No. 4,965,131. Silicon dioxide is preferred and is generally used in an amount ranging from about 1 to about 15 weight percent, based on the total solids employed. The size and concentration of the stabilizer particles determine the size of the final toner particles. In other words, the smaller the size and/or the higher the concentration of such particles, the smaller the size of the final toner particles.
Any suitable promoter that is water soluble and affects the hydrophilic/hydrophobic balance of the solid dispersing agent in the aqueous solution may be employed in order to drive the solid dispersing agent, that is, the particulate stabilizer, to the polymer/solvent droplet-water interface. Typical of such promoters are sulfonated polystyrenes, alginates, carboxymethyl cellulose, tetramethyl-ammonium hydroxide or chloride, 2-(diethylamino)ethyl methacrylate, water-soluble complex resinous amine condensation products of ethylene oxide, urea and formaldehyde, and polyethyleneimine. Also effective for this purpose are gelatin, casein, albumin, gluten and the like, or non-ionic materials such as methoxycellulose. The promoter is generally used in an amount from about 0.2 to about 0.6 parts per 100 parts of aqueous solution.
Various additives generally present in electrostatographic toner may be added to the polymer prior to dissolution in the solvent or in the dissolution step itself, such as waxes and lubricants.
The mixture of organic and aqueous phases is subjected to homogenization by high shear agitation, typically at ambient temperature, whereby the particulate stabilizer forms an interface between the organic globules in the organic phase. Due to the high surface area associated with small particles, the coverage by the particulate stabilizer is not complete. Coalescence continues until the surface is completely covered by particulate stabilizer. Thereafter, no further growth of the particles occurs. Accordingly, the amount of the particulate stabilizer is inversely proportional to the size of the toner obtained. The relationship between the aqueous phase and the organic phase, by volume may range from 1:1 to approximately 9:1. This indicates that the organic phase is typically present in an amount from about 10% to 50% of the total homogenized volume. Following the homogenization treatment, the solvent present is evaporated and the resultant product washed and dried.
As indicated, the present invention is applicable to the preparation of polymeric toner particles from any type of polymer that is capable of being dissolved in a solvent that is immiscible with water and includes compositions such as, for example, olefin homopolymers and copolymers, such as, polyethylene, polypropylene, polyisobutylene and polyisopentylene; polytrifluoroolefins, such as polytetrafluoroethylene and polytrifluorochloroethylene; polyamides, such as poly(hexamethylene adipamide), poly(hexamethylene sebacamide), and polycaprolactam; acrylic resins, such as poly(methyl methacrylate), poly(methyl acrylate), poly(ethyl methacrylate), styrene-methyl methacrylate copolymers, ethylene-methylacrylate copolymers, ethylene-ethyl acrylate copolymers, ethylene-ethyl methacrylate copolymers, polystyrene and copolymers of styrene with unsaturated monomers, cellulose derivatives, polyesters, polyvinyl resins, ethylene-allyl alcohol copolymers, and the like.
Pigments suitable for use in the practice of the present invention should be capable of being dispersed in the polymer, insoluble in water and yield strong permanent color. Typical of such pigments are the organic pigments such as phthalocyanines, lithols and the like and inorganic pigments such as TiO2, carbon black and the like. Typical of the phthalocyanine pigments are copper phthalocyanine, a monochlor copper phthalocyanine, and hexadecachlor copper phthalocyanine. Other organic pigments suitable for use herein include anthraquinone vat pigments such as vat yellow 6GLCL1127, quinone yellow 18-1, indanthrone CL1106, pyranthrone CL1096, brominated pyranthrones such as dibromopyranthrone, vat brilliant orange RK, anthramide brown CL1151, dibenzanthrone green CL1101, flavanthrone yellow CL1118; azo pigments such as toluidine red C169 and hansa yellow; and metallized pigments such as azo yellow and permanent red. The carbon black may be any of the known types such as channel black, furnace black, acetylene black, thermal black, lamp black and aniline black. The pigments are employed in an amount sufficient to give a content thereof in the toner from about 1 to about 40 weight percent, preferably about 4 to about 20 weight percent, based upon the weight of the toner.
Quaternary ammonium tetraphenylborate salts useful in the practice of the present invention are represented by the general formulas (I), (II), and (III), as described below: 
where R1 represents a substituted or unsubstituted alkyl or aryl group; R2 represents an alkylene or arylene group; R3, R4, and R5 each independently represents a substituted or unsubstituted alkyl group; and R3 and R4 taken together may represent a cyclic ring system; and R6 represents hydrogen or an alkyl group. Examples of R1 include methyl, ethyl, n-propyl, n-butyl, n-hexyl, undecyl, heptadecyl, phenyl, 4-methylphenyl, 4-t-butylphenyl, and the like. Examples of R2 include ethylene, 1,3-propylene, 1,4-butylene, hexamethylene, p-phenylene, and the like. Examples of R3, R4, and R5 include methyl, ethyl, propyl, octadecyl, benzyl, and the like, and R3 and R4 taken together may be 1,4-butylene, 1,5-pentylene, and the like. Examples of R6 include hydrogen, methyl, ethyl, n-propyl, n-butyl, octadecyl, benzyl, and the like. Preferably, R1 is undecyl, R2 is 1,3-propylene, R3 is methyl, R4 is methyl, R5 is benzyl and R6 is hydrogen. 
where R1 represents a substituted or unsubstituted alkyl or aryl group; R2 represents an alkylene or arylene group; R3, R4 and R5 each independently represents a substituted or unsubstituted alkyl group; and R3 and R4 taken together may represent a cyclic ring system. Examples of R1 include methyl, ethyl, n-propyl, n-butyl, n-hexyl, n-undecyl, n-heptadecyl, phenyl, 4-methylphenyl, 4-t-butylphenyl, and the like. Examples of R2 include ethylene, 1,3-propylene, 1,4-butylene, hexamethylene, p-phenylene, and the like. Examples of R3, R4 and R5 include methyl, ethyl, propyl, octadecyl, benzyl, and the like, and R3 and R4 taken together may be 1,4-butylene, 1,5-pentylene, and the like. Preferably, R1 is undecyl or phenyl, R2 is 1,3-propylene, R3 is methyl, R4 is methyl, and R5 is benzyl. 
where R1, R2, R3 and R4 each independently represents an alkyl or substituted alkyl group, and R1 and R2 taken together may represent a cyclic ring system. Examples of R1, R2, R3 and R4include methyl, ethyl, propyl, isopropyl, n-butyl, t-butyl, pentyl, hexyl, 2-ethylhexyl, heptyl, octyl, decyl, octadecyl, benzyl, 2-naphthylmethyl, and the like. Examples of R1 and R2 taken together include 1,4-butylene, 1,5-pentylene, and the like. Preferably, R1 and R2 are methyl, R3 is octadecyl, and R4 is 2-naphthylmethyl.
Tables 1 and 2 contain structures of representative compounds of the general formulas (I) and (III), respectively. Table 3 lists structures of representative compounds of the general formula (III).
In accordance with the present invention, the amount of quaternary ammonium tetraphenylborate salt in the toner particle composition comprises, preferably, about 0.1 to about 10 weight percent, more preferably, about 0.5 to about 5 weight percent of total solids.
Phosphonium salt polymers useful in the invention are condensation copolymers of the general formula (IV), formed by the condensation of at least one dicarboxylic acid or dicarboxylic ester monomer with at least one diol monomer, at least one of the acid or ester monomers including a triarylphosphonium salt group: 
where R1 represents a substituted or unsubstituted alkylene group, a substituted or unsubstituted 1,2-ethenyl group, or a substituted or unsubstituted arylene group; R2 represents a substituted or unsubstituted alkylene group or a substituted or unsubstituted arylene group; and R3 represents a substituted or unsubstituted alkyl group; Xxe2x88x92 represents an anion; m and n are mole percents totaling 100, based on total diacid or diester, where m has a value of 0.01 to 100; and xe2x80x94Oxe2x80x94R2xe2x80x94Oxe2x80x94 represents the radical of at least one diol monomer having a total mole percent, w, of 100, based on total diol.
Examples of R1 include ethylene, 1,3-propylene, 1,4-butylene, p-phenylene, m-phenylene, 1,2-ethenyl, 2,6-naphthalenyl, and the like; R2 is ethylene, 1,2-propylene, 1,4-butylene, 2,2-dimethyl-1,3-propylene, 1,4-cyclohexylenedimethylene, 2,2,4,4-tetramethyl-1,3-cyclobutylene, 4,4xe2x80x2-isopropylidenediphenylene(poly)oxyalkylene, p-phenylene(poly)oxyalkylene, and the like. The Xxe2x88x92 anion is tosylate, halide, tetraphenylborate, methosulfate, triflate, and the like. Preferably, R1 is 1,2-ethenyl, R2 is 4,4xe2x80x2-isopropylidenediphenylene(2.0)oxypropylene, R3 is methyl, Xxe2x88x92 is tosylate, m is 10, n is 90, and w is 100.